1. Field of the Invention
The present invention relates to a method for choosing the defect detection mode of an optical storage device, more particularly to a method for choosing the defect detection mode of an optical storage device before data are recorded on an optical storage medium.
2. Description of the Related Art
In the event of the existence of defects, for example, scratches, contamination and an intrinsic structural defect, in parts of an optical storage medium (such as a CD), predetermined data cannot be correctly stored on the parts of the optical storage medium. An attempt to read the stored data always ends in finding the data not retrievable and therefore not readable. In order to solve the aforesaid problem of finding unreadable data stored previously on the defective parts of an optical storage medium, related storage medium industry develops a kind of optical storage media with defect management, for example, re-writable CDs in Mount Rainier format, including commonly used CD-MRW discs and DAD+MAW discs.
It is necessary to develop the defect detection technology for identifying defective parts of an optical storage medium so as to ensure the completeness of the data intended for storage. The defect detection technology essentially involves two modes, namely write detection and write verification. In a write detection mode, a servo defect detection signal, which is generated when data is recorded on the optical storage medium, is compared with a default threshold value, as shown in Step 11, Step 12 and Step 13 of FIG. 1. If the servo defect detection signal is higher than the threshold value, then the servo defect detection signal is converted into a defect ELM (Eight to Fourteen Modulation; 8-14 Modulation) signal, as shown in Step 14. Afterward, the defect ELM signal is converted into a defect block by decoding, as shown in Step 15; in other words, a physical defect address is replaced with a logical defect address. If the servo defect detection signal is lower than the threshold value, then Step 16 follows Step 13 before the process continues. If the data have not yet been completely written on the optical storage medium, Step 16 is followed by a return to Step 12. Step 17 follows Step 16 only after all the data are completely stored. Then the whole process ends.
FIG. 2 is a flow chart about writing data under a write verification mode in accordance with a conventional defect detection technology. As shown in Step 21, data are written on an optical storage medium first. In Step 22, part of the data are written in a data block. After writing the part of the data, whether the written data can be read out from the data block is confirmed, as shown in Step 23. If the written data cannot be read, the process flow proceeds to Step 24 and labels the data block as a defect block. Conversely, if the written data can be read, Step 25 is proceeded directly. In Step 25, whether the data block has been totally read is confirmed; if the data block has not yet been totally read, Step 23 is proceeded again to repeat the aforesaid steps. Otherwise, Step 26 is proceeded to confirm whether the data have been completely written on the optical storage medium. As shown in Step 27, the entire process does not end unless and until all the data are stored; otherwise, Step 22 is proceeded again to write the other unrecorded part of the data.
The write detection mode involves comparing a servo defect detection signal generated when data are written, such as an IF Signal or a Sub-Beam Add (SAD) Signal, with a threshold value directly, to quickly determine whether any defect is present in the current block. However, since a servo defect detection signal is usually a signal that results from retrieval of light reflection, it is rather difficult to decide on an optimal threshold value suitable for various status of defects; for example, reflective conditions vary with the area of a defect, a fingerprint contamination, or a scratch.
With the step of reading the written data, the write verification mode involves verifying repeatedly whether any defect is present. Hence, the write verification mode does identify defects efficiently, compared to the write detection mode that involves simple steps. Nevertheless, the write verification mode is time-consuming as it involves more steps.
To sum up, the conventional defect detection technology can merely choose either a write detection mode or a write verification mode to debug errors. Therefore, it does not assure an optical storage device of two merits, namely speediness and reliability, equally well, nor does it allow the defect detection mode of the optical storage device to be flexibly adjusted according to the actual locations of defects present in an optical storage medium.